Apparatus for determining the shape and/or size of little particles

ABSTRACT

The invention relates to an apparatus for determining the shape and/or size of small particles, comprising a cell into which the particles are placed, at least one light source for illuminating the particles, and at least one one-dimensional image sensor for measuring an image of the illuminated particles. The cell is embodied as a conduit through which the particles can be transported, and the image sensor is placed in the immediate vicinity of the conduit or into the conduit.

[0001] The invention relates to an apparatus for determining the shape and/or size of small particles, comprising a cell into which the particles are placed, at least one light source for illuminating the particles, and at least one one-dimensional image sensor for measuring an image of the illuminated particles. Within the frame of the present invention, small particles are understood to be particles having a size of up to 200 μm in diameter.

[0002] From the prior art various instruments are known with which the size or shape of particles can be determined. However, the problem with these known devices is, that they are complex and expensive, and that the shape of the particles is determined in a very indirect manner and therefore does not provide any direct information with regard to shape.

[0003] From U.S. Pat. No. 5,764,358 a method and apparatus is known for the determination of the shape characteristics of particles, which particles are fed through a transparent cell through which a light beam is projected. The intensity of the light scattered by the particles is measured with a detector comprising one or more concentric rings or parts of rings, at least one of which is provided with one or more isolated segments. The rings and the isolated segments are coupled to an energy meter for the determination of amplitude classes. The shape characteristics of the particles are determined on the basis of the thus provided amplitude classes.

[0004] U.S. Pat. No. 4,070,113 relates to a system for classifying the various types of blood cells by using a laser beam. The light scattered by the blood cells is applied to a detector array, which provides a voltage spectrum that is representative of the spatial relationship of the cells. This voltage spectrum is compared with known spectra that are representative of different blood cell classes. When a good fit is found, the blood cell is assigned to the respective blood cell class.

[0005] U.S. Pat. No. 4,173,415 relates to a method and apparatus for rapidly characterizing and differentiating large organic cells. To this end individual cells are illuminated with monochromatic light, which produces a light-scattering pattern that is measured with the aid of an array of detectors. The resulting measurement is used for the identification and characterization of the cell.

[0006] Characteristic of the above-discussed prior art is that use is made of the scattering of the light with which the particles to be analyzed are illuminated. The image obtained at the detector array is per definition an imprecise image so that the determination of the particle shape, though not impossible, is laborious and exhibits considerable inaccuracies.

[0007] U.S. Pat. No. 5,548,395 relates to an apparatus for analyzing particles, wherein a one-dimensional image sensor is used which extends transversely to the flow direction of the particles, and which serves to catch images of the shadows of the particles that are illuminated by a light beam, for example, a laser beam.

[0008] From U.S. Pat. No. 5,572,320 an apparatus for the classification of particles is known, wherein the particles are fed through a conduit and wherein a light source that is oriented transversely to the conduit, illuminates the particles. With the aid of an optical system the resulting shadows from the particles are detected by an image sensor provided behind the optical system. The optical system serves to enlarge the shadows to allow a desirable resolution to be realized. The conduit applied in U.S. Pat. No. 5,572,320 is sufficiently thin that the diffraction pattern of light exiting it is characteristic of the optical near field. Correspondingly, the preamble of claim 1 reads on U.S. Pat. No. 5,572,320.

[0009] It is the object of the invention to provide an apparatus with which it is possible to obtain information about the shape and size of individual particles quickly and simply, that is to say without the need of numerous complicated calculations on the basis of the measured images. The object is also to provide a relatively simple apparatus.

[0010] The apparatus according to the invention is characterized in that the same is provided with multiple light sources and image sensors that are grouped around the conduit to enable them to form the image. The inventors describe this apparatus of a next generation as a small aperture straight through a (silicon) slice of, for example, 0.5 mm thickness, wherein a two-dimensional shot is taken (tomography) by means of light sources and photodiodes around the rim of the aperture.

[0011] The moment a particle flows through the light beam, a cast shadow will fall on one or several light-sensitive elements of the image sensor. Preferably the light sensitive elements are read out repeatedly, and the shape and/or size of the particles is derived from a combination of the thus repeatedly carried out measurement. The result, after applying a few simple computations is—as it were—a photo-record of the particle.

[0012] An essential aspect of the invention is that the light sensitive elements are located in the so-called near field (Fresnel zone) of the particles, so that a direct optical record is obtained of the particles, while avoiding the influence of scattering light. An important advantage provided by the invention in comparison with the prior art is that it makes it possible to determine the size and shape of each individual particle. The apparatus to be used for this purpose can be realized inexpensively and its operation is simple. An optical system for the registration of the particles is not necessary.

[0013] In order to ensure that the image sensor is located in the near field the conduit used may, for example, be a conduit that is so small that the particles are bound to be in the right position. However, within the frame of the invention it is also conceivable to use a conduit in which hydrodynamic focusing occurs with which the stream of particles may be positioned on a previously determined location in the conduit. It is also conceivable to apply a different external force for the positioning of the particles.

[0014] The conduit may be made of, for example, silicon or glass. The light source then provides light that is directed transversely to the conduit, in the direction of the image sensor. There is no need to use an optical system for the registration of the particles.

[0015] For the one-dimensional image sensor there are various possible implementations. For example, an array of photodiodes, CCD elements, phototransistors, and the like may be used. A suitable embodiment of the apparatus is characterized in that the image sensor comprises a structure of elongated photosensitive elements that are placed in the conduit and substantially at right angles to the flow of particles through the conduit.

[0016] An alternative embodiment is characterized in that the image sensor comprises a one-dimensional array of light-sensitive elements that are placed into the conduit, and substantially at right angles to the flow of particles through the conduit. Advantageously the image sensor is embodied such that it comprises two one-dimensional arrays of light-sensitive elements placed one behind the other in the conduit, and substantially at right angles to the flow of the particles through the conduit. This endows the image sensor with a greater robustness, while in addition providing a higher resolution. In this manner it is also possible to determine the speed of the particles.

[0017] This may be achieved in particular if the image sensor is embodied such that, viewed in the flow direction, the light-sensitive elements of the first array are placed next to the light-sensitive elements of the second array.

[0018] In another aspect of the invention, the apparatus is characterized in that the same comprises a plurality of conduits arranged next to each other, each of them provided with at least one image sensor.

[0019] The fact that the apparatus according to the invention is especially suitable to be embodied in an integrated circuit, makes it possible in this manner to provide an apparatus that is capable of quickly analyzing large quantities of particles by processing them parallel with the thus embodied apparatus. This is especially useful with medical applications, where it is necessary for large numbers of cells to be analyzed in a short time.

[0020] In a further proposed embodiment variant, the apparatus may advantageously be embodied such that the same comprises a selection actuator for directing particles through one of the conduits. This provides a system of so-called sample enrichment, in which large quantities of particles can be analyzed automatically, and particles deviating from a predetermined standard can be selected to be separately further analyzed in more detail.

[0021] It is believed that the afore-given description of the invention is sufficiently clear and complete for a person skilled in the art, so that further elucidation based on an Example or the like may be omitted. It is further remarked, that the above description contains an elucidation with regard to the appended claims, without in any way limiting the protective scope derived from these claims. 

What is claimed is:
 1. An apparatus for determining the shape and/or size of small particles, comprising a conduit through which the particles can be transported, at least one light source for illuminating the particles, and at least one one-dimensional image sensor for measuring an image of the illuminated particles which is placed in the immediate vicinity of the conduit, in the near field (Fresnel zone) of the particles, wherein the apparatus comprises multiple light sources and image sensors that are grouped around the conduit for the formation of the image.
 2. An apparatus according to claim 1, wherein the image sensor comprises a structure of elongated photosensitive elements that are placed in the conduit and substantially at right angles to the flow of particles through the conduit.
 3. An apparatus according to claim 1, wherein the image sensor comprises at least one one-dimensional array of light-sensitive elements that are placed into the conduit, and substantially at right angles to the flow of particles through the conduit.
 4. An apparatus according to claim 1, wherein the image sensor comprises two one-dimensional arrays of light-sensitive elements placed one behind the other in the conduit, and substantially at right angles to the flow of the particles through the conduit.
 5. An apparatus according to claim 4, wherein viewed in the flow direction, the light-sensitive elements of the first array are placed next to the light-sensitive elements of the second array.
 6. An apparatus according to claim 1, wherein the apparatus comprises a plurality of conduits arranged next to each other, each of them provided with at least one image sensor.
 7. An apparatus according to claim 6, wherein the apparatus comprises a selection actuator for directing particles through one of the conduits. 